Self-supporting coaxial cable



Feb. 25, 1969 D. c. ALEXANDER SELF-SUPPORTING CQAXIAL CABLE Filed April 20, 1967 INVENTOR. non/A40 c. ALEXAA/OER United States Patent Claims ABSTRACT OF THE DISCLOSURE A coaxial cable includes an inner conductor surrounded by a first dielectric layer, a metallic shield around the first dielectric, a second dielectric layer around the shield, a permeable material around the second dielectric and an outer dielectric layer around the permeable material. An adhesive is applied to the permeable material to provide a bond to the outer dielectric but does not prevent movement of the permeable material with respect to the second dielectric and other inner layers. The bond. strengthens the outer layer to provide a self-supporting structure while maintaining flexibility of the full cable. Another pair of conductors parallel to the coaxial cable may be included within an adjoining portion of the outer dielectric with a web therebetween.

Background of invention This invention relates to cables and particularly to a self-supporting combination coaxial cable-audio pair.

In cables which contain single purpose conductors or multipurpose elements, such as the subject of this invention, for instance, and which are designed to be supported from poles or similar support, it has been the practice to eliminate or reduce the strain on such cables by running parallel with the cable either inside the outer dielectric covering or outside it but closely adjacent thereto, a high strength but low conductivity wire or cable, which serves to support the conducting cable. It is also known to make coaxial cables in the form of a figure 8 with one lobe carrying a messenger cable; in this case, in effect, one half of the cable is for strength. In either case, the inclusion of a separate cable for sup porting purpose only tends to make the cable more costly and bulky, and also considerably reduces the flexibility of the cable; the flexibility being desirable for adjusting to sharp bends and ease of handling. This requirement is important in the case of a multipurpose cable, such as the invention herein, which contains both a coaxial cable of the type used for CATV (community antenna television) and a telephone pair. By combining the two single purpose cables into one cable structure it is possible to achieve a single unit which is less costly and more compact. This type of cable is useful where it is necessary to make connection from the main telephone line and a main CATV line which are carried on the same supporting structure, in most cases above ground, to a subscriber who is using both telephone service and CATV service.

It is therefore an object of this invention to provide a single structure cable which includes both a coaxial cable and at least one telephone pair in the same cable structure which has a high degree of flexibility, is selfsupporting and 'is relatively inexpensive to produce.

The above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

FIGURE 1 shows a cross-section transverse view of the cable structure of this invention; and

FIGURE 2 shows a longitudinal view of the cable structure.

With reference to the figures, there is shown a first portion 1 which is the coaxial section of the cable and a second portion 2 which comprises at least one telephone pair Which is the second portion of the combined cable. The telephone pair is, of course, parallel to the coaxial cable. The two portions which are enclosed within the same dielectric outer jacket are connected by a web 3 of the same dielectric. The component portions of the coaxial cable section 1 comprise an inner conductor 4, a primary dielectric 5 surrounding the inner conductor which may be, for instance, polyethylene or any other suitable dielectric, a metallic shield 6 which constitutes the outer conductor of the coaxial cable and which may be made of tinned copper, for example, or any other suitable material; it may be braided or a tape wrapped longi tudinally or spirally. Surrounding the shield 6 is a dielectric separator 7 and the preferred material, though not necessarily the only one suitable for this purpose, is Mylar (polyethylene terephthalate) which has both good dielectric properties and high strength. The dielectric separator 7 may be in the form of a tape which is wrapped around the shield 6. A permeable fibrous braid 8 of non-metallic material, preferably glass, is then disposed about the separator 7. The telephone pair section of the cable comprises standard telephone wire which has two conductors 9, a primary dielectric 10 for each conductor and is disposed as a twisted pair. About the twisted pair is wound a dielectric tape or hinder 11 such as Mylar (polyethylene terephthalate). Although only one telephone pair is shown in the drawings, it is, of course, possible to have more than one telephone pair where needed. An integral outer dielectric sheath 15 surrounds both the coaxial cable and the telephone pair. Both sections of the cable are joined by the web 3 which is integral with the two parts of the outer sheath 15. The dielectric sheath 15 may be made of polyvinyl chloride, polyethylene, neoprene or any other suitable polymeric insulating material.

In order to provide a flexible construction and add strength to the cable, the braid 8 is treated so that it will adhere to the outer jacket 15 but will not adhere to the tape or separator 7 and in any flexing of the cable the outer sheath 15 with the fibrous braid attached thereto will move relative to the remainder of the cable. To achieve this flexibility, the fibrous braid 8 which is preferably a glass braid is treated with an adhesive which may be a ketone solution of a synthetic rubber of the acrylonitrile/butadiene type compounded with conventional additives such as fillers, stabilizers, and antioxidants, and combined with a phenolic resin. Such an adhesive is sold by the Angier Adhesive Division of Interchemical Corporation under the name SBS-404-l30 Tie- Coat. In the application of the adhesive, the wire to be coated which is now complete with the exception of the outer jacket 15 is passed through a vessel containing the adhesive solution so as to cause the braid to become completely immersed in and to be impregnated with the adhesive solution. It is then drawn through a flexible orifice of a size to accommodate the wire but still elfect a wiping action of the wire so as to remove excess adhesive solution. The wire so treated is then passed through a heated chamber at a temperature of 200300 F. to remove the solvent and leave as a coating on the fibrous braid the solid portion of the adhesive solution. The nature of the adhesive is such that when so dried and subsequently cooled to room temperature, it has only a slight tackiness and does not block or cause sticking of adjacent layers of wire on a spool. When the hot plastic jacketing material 15 is applied over the adhesive coated wire it causes the development of an adhesive bond between the jacket material and the adhesive coated fibrous substrate 8. The fibrous substrate 8, however, is not bonded to the separator 7; therefore, in any flexing of the cable the bonded substrate 8 and outer jacket 15 is able to slide over the separator 7.

The effect of bonding the fibrous substrate 8 to the jacket material is to provide suflicient strength for selfsupport of the cable without the necessity of an outer strength member. The fibrous substrate 8 is a strength member and by bonding it to the jacket 15 there is a transfer of the substrate strength to the jacket. Without bonding to the fibrous substrate the jacket alone would not be a strength member and when subjected to longitudinal pull it would stretch and slide off the core. The high strength substrate firmly bonded to the jacket greatly reduces the jacket stretch but does not reduce cable flexibility. Thus the bonding of the substrate to the jacket creates a flexible, sag resistant tube with sufficient strength to self-support the cable when it is suspended between two points.

Another method of bonding the fibrous substrate to the outer jacket is to extrude or otherwise apply a thin layer of polyethylene over the fibrous substrate and then apply heat to soften or melt the polyethylene as it enters the extruding machine Where the jacket dielectric is extruded over the fibrous substrate, thereby firmly bonding the substrate to the neoprene.

Although I have described a combined coaxial and audio pair cable, it is obvious that the cable construction described is suitable for a coaxial cable only, as the novel strength and flexibility features are incorporated therein.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

1. A coaxial cable comprising an inner conductor, a dielectric surrounding said inner conductor, a metallic shield surrounding said dielectric, a dielectric separator surrounding said shield, a permeable material disposed about said dielectric separator, an outer dielectric layer surrounding said permeable material, and means disposed about said permeable material bonding said permeable material to said outer dielectric layer but not preventing movement of said permeable material and said outer dielectric layer about said dielectric separator.

2. A cable according to claim 1 wherein said permeable material is fibrous.

3. A cable according to claim 1 wherein said permeable material is glass.

4. A cable according to claim 1 wherein said means disposed about said permeable material is an adhesive substance.

5. A cable according to claim 4 wherein said adhesive substance comprises a ketone solution of a synthetic rubber of the acrylonitrile/butadiene type combined with phenolic resin.

6. A cable according to claim 1 wherein said dielectric separator is polyethylene terephthalate.

7. A cable according to claim 1 wherein said means disposed about said permeable material is polyethylene.

8. A combination coaxial cable and audio pair comprising a coaxial portion and an audio pair portion disposed parallel to said first coaxial portion, said first coaxial portion comprising an inner conductor, a dielectric surroundin said inner conductor, a metallic shield surrounding said dielectric, a dielectric separator surrounding said shield, a permeable material disposed about said dielectric separator and an integral outer dielectric layer surrounding said permeable material and said audio pair, means disposed about said permeable material to cause said permeable material to adhere to said outer; dielectric layer but capable of movement about said dielectric separator.

References Cited UNITED STATES PATENTS 2,956,613 10/1960 Edelman l74121 X 3,328,510 6/1967 White 17417X LEWIS H. MYERS, Primary Examiner.

ELLIOT GOLDBERG, Assistant Exwminer.

US. Cl. X.R. 174-107, 121 

